The incorporation of a variety of polymers in particulate detergent compositions for a variety of reasons is well-known. Polymers may be incorporated, in particular, as builders and sequestrants, and as soil release agents. Examples of builder polymers include polycarboxylates, for example, acrylate and acrylate/maleate polymers; examples of soil release polymers include polyethylene glycol/polyvinyl acetate graft copolymers, and soil release polyesters derived from terephthalic acid and polyethylene glycol.
Detergent-functional polymers for incorporation into detergent powders are generally supplied as aqueous solutions of various concentrations. In the aqueous solutions, the water has no function other than lowering the viscosity during and after the polymerisation process. If it is surplus to the requirements of the final detergent product, it must be removed by the detergent manufacturer either before or during its incorporation into products.
Traditional low- and medium-density detergent powders were and are prepared by spray-drying an aqueous slurry of all ingredients that are sufficiently heat-insensitive, including most detergent-functional polymers. This is a high temperature process in which large amounts of water are driven off. In this process the water associated with the polymer is a minor contributor to the total slurry moisture and makes little or no difference to the efficiency or energy consumption of the process.
The compact or concentrated powders which now form a substantial part of the market, however, are prepared by non-tower mixing and granulation processes which generally avoid high-temperature processing where water will be driven off.
In such processes it is generally desirable that the moisture content should be kept as low as possible, both to facilitate granulation, which requires a carefully controlled balance of liquid and solid ingredients, and to ensure that the final product also has as low as possible a moisture content. Low moisture content is especially important for compositions to which moisture-sensitive bleach ingredients, especially sodium percarbonate, are to be added.
Mixing and granulation may be followed by a separate drying step, for example, in a fluidised bed, but that requires additional plant and the expenditure of additional energy.
Accordingly, in the preparation of compact high bulk density powders, the incorporation of polymers in the form of aqueous solutions is not ideal. Only small amounts can be used before processing behaviour is affected detrimentally; and the resulting powders have also been found to leave residues on washloads.
Simply drying the aqueous polymer solution itself, in an attempt to obtain a dry 100% polymer material, is not an option for most polymers because it results in a gel, a sticky or rubbery mass or a hygroscopic material which is difficult or impossible to handle. The drying itself is also difficult and energy-intensive.
A possible alternative approach is to dry the aqueous polymer solution in combination with other materials, notably inorganic or organic salts, but this method too has encountered problems. The use of soluble salts can lead to salting-out of the polymer in rubbery lumps and balls, while inorganic salts such as zeolite give products which are very slow to disintegrate and dissolve in the wash; this route tends to produce only materials with low levels of polymer (10 wt % or below); and again an energy-intensive drying step is needed.
It has now been found that detergent-functional polymers may be easily and successfully incorporated in particulate detergent compositions or components in the form of a non-aqueous liquid premix, that is to say, a premix produced by a process in which a non-aqueous diluent has been used instead of water to reduce the viscosity of the polymer during the polymerisation process.
EP 622 454A (Procter & Gamble) discloses structured pumpable nonionic surfactant premixes containing, as structuring agents, certain polymers derived from hydroxyl-group-containing monomers, or polyvinyl pyrrolidone or polyvinyl pyridine-N-oxide, or sugars or artificial sweeteners. The premixes may contain substantial quantities of water. The premixes are used in the preparation of granular laundry detergent compositions components of high bulk density containing nonionic surfactants.